THE BIOLOGICAL ACTIVITIES OF BACTERIA 47 



For our knowledge of the fundamental laws underlying these 

 phenomena of fermentation and protein decomposition, we are in- 

 debted to the genius of Pasteur, 1 who was the first to prove experi- 

 mentally the exclusive and specific parts played by various microor- 

 ganisms in these processes. While the observations and deductions 

 made by Pasteur have not been greatly modified, a large store of in- 

 formation has been gained since his time, which has thrown addi- 

 tional light upon the chemical details and the more exact manner of 

 action of the factors involved. 



The actual work of cleavage in both fermentation and protein 

 cleavage is carried out by substances known as enzymes or ferments, 

 the nature of which we must further discuss before their manner of 

 action can be fully comprehended. 



Bacterial Enzymes or Ferments. A ferment or enzyme is a sub- 

 stance produced by a living cell, which brings about a chemical re- 

 action without entering into the reaction itself. The enzyme itself is 

 not bound to any of the end products and is not appreciably dimin- 

 ished in quantity after the reaction is over, although its activity may 

 be finally inhibited by one or another of the new products. The action 

 of bacterial enzymes is thus seen to be closely similar to that of the 

 chemical agents technically spoken of as ' Catalyzers," represented 

 chiefly by dilute acids. Thus, if an aqueous solution of saccharose is 

 brought into contact with a dilute solution of sulphuric acid, the di- 

 saccharid is hydrolyzed and is decomposed into levulose and dextrose. 



Thus : 



C^H^O,, + H 2 C 6 H 12 6 + C 6 H 12 G 

 In contact with Dextrose Levulose 



dilute H 2 S0 4 



During this process, which is known as ''inversion," the concentra- 

 tion of the sulphuric acid remains entirely unchanged. While theo- 

 retically the changes brought about by enzymes and katalyzers are 

 usually such as would occur spontaneously, the time for the sponta- 

 neous occurrence would be, at ordinary temperatures, infinitely long. 

 The definition for enzymes and katalyzers is given by Ostwald, there- 

 fore, as "substances which hasten a chemical reaction without them- 

 selves taking part in it. ' ' Exactly the same result which is obtained 

 by the use of dilute sulphuric acid is caused by the ferment "inver- 

 tasc" produced, for instance, by B. megatherium. Were a solution 



1 Pasteur, ''Etude sur la biere," Paris, 1876. 



